Fluid mechanics isn’t taught at A level, so here are some of the concepts you’ll learn at university.

**Buoyancy**

Fluids exert an upwards force equal to the weight of the displaced fluid. This is called Archimedes’ principle. This can be shown on a free body diagram:

**Fluid flow**

Fluid flow can be represented by flow lines, which should the path of a particle in the flow:

Stream lines are curves whose tangent gives the velocity. When the flow lines and the stream lines are the same the flow is steady.

The mass of water entering a pipe must be equal to the mass leaving. This gives us:

This is called the continuity equation.

**Bernoulli’s equation**

We can use conservation of energy to derive Bernoulli’s equation:

This can be used to find velocity, height etc, but breaks down when there is viscosity.

**Pascal’s law**

This can be derived using a small layer of non compressible fluid:

At equilibrium the sum of the forces is zero:

This result is Pascal’s law.

Pressure applied is transmitted to every part of the fluid, so pressure, *p*, is the same at all points of the same height.

This means that heavy objects can be raised using hydraulic lift as force varies with area:

Gauge pressure = absolute pressure – atmospheric pressure

Back to Contents: Physics: Mechanics

### Like this:

Like Loading...